1. Field of the Invention
The present invention relates to an optical system supporting mechanism for moving the optical system by which a document of a document reading device in an image processing equipment such as a copying machine or a printer is exposed to light and scanned.
2. Description of the Prior Art
The general construction and the principle of a document reading device are explained with reference to FIG. 6. According to FIG. 6, a document 53 placed on a document set plate 52 is exposed to the light source 51 and scanned thereby.
The light source 51 and the first mirror 54 are so composed that they can move as a body from the position shown with the solid lines to that shown with the dashed lines in FIG. 6.
The second mirror 55 and the third mirror 56 are also so composed that they can move as a body from the position shown with the solid lines to that shown with the dotted lines in FIG. 6.
When the light source 51 and the first mirror 54 move in the direction of an arrow "A" from the position shown with the solid lines in FIG. 6, the second mirror 55 and the third mirror 56 also move at half the speed of the light source 51 and etc. in the same direction from the position shown with the solid lines in FIG. 6, while accompanying with the light source 51 and the first mirror 54.
Such an optical system as shown in the above is supported on the guide shaft 65 movably along therewith by means of the moving units 60a and 60b respectively shown in FIG. 7. Namely, the light source 51 and the first mirror 54 are mounted at one moving unit 60a, and furthermore the second mirror 55 and the third mirror 56 are mounted on the other moving unit 60b. Thus, the optical system travels along the guide shaft 65.
However, the moving unit 60a on which the light source 51, etc. are placed is so composed that the unit 60a can travel at a speed two times that of the moving unit 60b on which the second mirror 55, etc. are placed.
As the document reading device 59 is so composed as being shown in the above, the reflection light which is produced according to the result of shedding light on the document 52 by the light source 51 forms an image on the line sensor 58 consisting of CCD, etc. with the inclusion of the first mirror 54, the second mirror 55, the third mirror 56, and lens 57 which can collect this reflection light.
FIG. 7 shows the moving units 60a and 60b (hereinafter merely called the moving unit 60, including the moving units 60a and 60b) of the conventional optical system supporting mechanism which supports the optical system and moves along the guide shaft 65.
The conventional moving unit 60 is provided with at least two guide rollers 63, which are one of the examples of the first guide members and which move along the guide shaft 65.
Also, the pusher rollers 64 and 64 which are one of the examples of the second guide members are provided so that they can be placed in the opposite side of the guide rollers 63 and 63, putting the guide shaft 65 therebetween.
In addition, the moving unit 60 is provided with arms 67 rotatable around the arm supporting shafts 66 which are placed with the right angle to the guide shaft 65, corresponding to the pusher rollers 64, respectively. And the pusher rollers 64 are attached to the end portions of the arms 67.
Furthermore, these arms 67 are elastically energy-charged by means of springs 68 so that the pusher rollers 64 can be pushed against the guide shaft 65.
Therefore, as the guide shaft 65 is between the guide rollers 63 and the pusher rollers 64, the travelling unit 60 can be so supported by these rollers as the unit 60 can freely move along the guide shaft 65.
Also in the case that the guide rollers 63 and the pusher rollers 64 are worn and made small in diameter due to aging changes, etc., the pusher rollers 64 are pushed against the guide shaft 65 by means of the springs 68, and the guide shaft 65 is accordingly between the guide rollers 63 and the pusher rollers 64. Therefore, also in this case, the travelling unit 60 can be so supported by these rollers that the unit 60 can freely travel along the guide shaft 65.
It is necessry for the travelling unit 60 to be so composed that the travelling unit 60 can not be parted from the guide shaft 65, in order to prevent image reading from adverse influence which may be produced by large vibration which occurs due to reciprocating movements of the optical system having a considerable weight. For this reason, in order to control the direction of rotation of the arms 67 which moves around the arm supporting shafts 66, one-way clutches 69a and 69b which can permit normal rotation thereof but can not permit reverse rotation thereof are installed at the arm supporting shafts 66 and 66, thereby causing the pressure thereof against the guide shaft 65 to be enhanced. (However, the permitted direction or the prevented direction of the one-way clutch 69a and another one-way clutch 69b becomes reversed to each other).
Therefore, when the spring 68 is about to be elongated as a result of vibrations by the moving unit 60 due to starting and stopping of moving thereof, the arms 67 can move only in the contracting direction of the spring 68 by means of the one-way clutches 69a and 69b.
Therefore, the moving unit 60 can be supported without any rise due to the above vibrations.
Such an optical system supporting mechanism as shown in the above is disclosed by, for instance, the Japanese Laid-Open Pat. Pub. Sho-61-158350.
In the optical system supporting mechanism of the conventional image processing equipment, as one-way clutches are provided in order to prevent the above rising phenomena, the structure thereof may become complicated, thereby causing the cost of production to be increased.
Also, in the case that the moving unit is removed from the guide shaft as the one-way clutch inherently rotates in one direction, the moving unit must be removed together with the arms, etc., at the same time. Therefore, it may become difficult to carry out the maintenance through disassembling.
Furthermore, as usually an one-way clutch has some play, it is difficult for vibration to be sufficiently suppressed.